GM22923 is concerned with development of nitroxide radical "spin-label" electron spin resonance (ESR) methodology. In this competitive renewal for years -14 to -18, focus is on measurements of bimolecular collision rates between (a) spin labels and molecular oxygen (so-called spin-label oximetry), (b) between spin labels and organo-metallic complexes and (c) between spin-labeled biomolecules that contain the 14N isotope and those that contain the 15N isotope. The experiments are based on pulse ESR techniques and computer deconvolution of the resulting multiexponential saturation-recovery signals as developed in the previous funding period. Engineering refinements of the existing high speed signal acquisition equipment are proposed in order to minimize instrumental distortion of transient signals. Essentially all experiments involve synthetic lipid bilayerrs and biological membranes. Most previous spin- label experiments in membranes were concerned with rotational processes, but translational processes studied here through the measurement of bimolecular collision rates are felt to be more biologically relevant. A method has been devised to determine for the first time the oxygen permeability of a membrane. Oxygen transport across the membrane is crucial to cellular respiration. In other studies, rate consants for physical exchange between lipids in two environments in heterogeneous membraneous systems will be measured. Further development of "multifrequency saturation- recovery" equipment will be carried out: namely, construction of a K-band pulse accessory to supplement existing X-band and "under-construction" S- band pulse equipment. Multifrequency saturation-recovery capability will be useful for two purposes: (1) measurement of dipolar non-secular contributtions to spin-label relaxation in fluids, which will improve the quality of the data on bimolecular collisions (this information arises primarily from Heisenberg exchange, but can be confounded by dipolar contributions), and (2) measurement of distances of closest approach between spin labels in membranes and metal ions on the membran surface. A considerable amount of organic synthesis of novel spin labels, organo- metallic compounds and 15 N- substituted spin labels is proposed including synthesis of phospholipids with metal-ion chelation groups attached to the phosphate groups. This is an interdisciplinary program involving physicists, biochemists, biophysicists, chemists, and engineers at the National Biomedical ESR Center.